Remediation of a heavy metal-contaminated soil by a rhamnolipid foam

Studies were initiated with a rhamnolipid biosurfactant in columns to simulate in situ soil remediation conditions. The biosurfactant was injected in the form of a foam and liquid solution. The study was conducted in three steps: evaluation of the foam characteristics, investigation of pressure buildup by foam injection and the removal of metals by the foam. Foam quality of the rhamnolipid was shown to vary between 90% and 99% with stabilities from 17 to 41 min. Pressure buildup was then evaluated with different flow rates, foam quality and concentration of the biosurfactant solutions. Metal removal was then evaluated from a sandy soil contaminated with 1710 ppm of Cd and 2010 ppm of Ni. Maximum removal was obtained by a foam produced by 0.5% rhamnolipid solution after 20 pore volumes. Removal efficiency for the biosurfactant foam was 73.2% of Cd and 68.1% of Ni. With the biosurfactant liquid solution, 61.7% Cd and 51.0% were removed. Distilled water removed only 18% of both Cd and Ni. Concentrations of 0.5%, 1.0% and 1.5% rhamnolipid at pH values of 6.8, 8 and 10 were also evaluated but the effect of pH did not show significant effects. Therefore, rhamnolipid foam may be an effective and non-toxic method of remediating heavy metal-contaminated soils. Further efforts will be required to optimize the performance of the foam.